It is well known in the art to provide a window having more than one pane of glass, the panes being separated by an airspace. Such windows are known as insulating windows or insulated glass panels by virtue of the fact that the air or other gaseous material (argon, helium, nitrogen, et cetera) trapped within the space between the glass panes serves as an insulator to reduce heat flow through the glass. Typically, the glass panes are separated by a spacer frame comprised of sections of tubing joined together at adjacent ends to form a continuous frame. The spacer frame lies between the glass panes and extends around their perimeter. The tubes comprising the spacer frame, also known as spacer-frame bars, are commonly made of aluminum or metals, such as steel or stainless steel, since, in addition to being commercially economical, these materials are sufficiently strong and rigid to permit the tubes to function as spacer-frame bars. Also, aluminum and steel exhibit good corrosion resistance, and their structural integrity is not adversely affected by long-term exposure to sunlight.
In order to keep the air trapped within the space between the glass panes as dry as possible to prevent the glass panes from fogging, it is essential that the spacer frames be and remain hermetically attached to the glass panes throughout the expected life of the insulated glass panels. To assure a hermetic bond between the spacer frames and the glass panes, a mastic-like sealant material is generally heated and applied to the outside faces of the spacer frames where it flows into sealing and bonding contact between the glass and the spacer-frame bars. Alternately, the hermetic bond can be formed by application of a two-part sealant consisting of a resinous adhesive and a catalyst that reacts with the adhesive to cure the sealant. This process typically requires contriver between the spacer-frame bars and the glass panes to maintain structural strength in the insulated glass panels and to prevent seepage of the heated sealant material beyond the spacer-frame bars and onto the visible portions of the insulated glass panels.
Since the introduction of insulated glass panels, great benefits have been derived in the form of diminished heat loss and increased energy savings based on the insulation effect provided by the air trapped between the glass panes. So great has that savings been that little thought was given to additional areas of heat loss within the insulated glass panels. It has since been realized that, despite representing a relatively small percentage of the entire insulated glass panel, the physical contact between the spacer-frame bars and the glass panes results in substantial energy loss through the area of the frame. The spacer-frame bars, metallic in nature and highly heat conductive, act to transfer energy between the glass panes with obvious heat-loss implications.